1. Field of the Invention
The invention relates to a lighting arrangement which is provided in particular for the interior lighting in a vehicle or aircraft, in particular in a passenger aircraft.
Hitherto fluorescent lamps have predominantly been used for illuminating the interior of an aircraft. With the exclusive use of fluorescent lamps however it is only very limitedly possible to alter the brightness of the interior lighting or to vary the colour spectrum thereof. That is found to be a disadvantage in many situations. In particular in the design of a modern lighting arrangement in aircraft engineering so-called ‘mood lighting’ is increasingly used. In that respect use is made of the realisation that the mood and thus the wellbeing of the aircraft passengers, in particular during a long intercontinental flight, can be positively influenced by adapting the interior lighting to the daytime situation. Thus for example interior lighting with a high proportion of blue has a calming effect and can thus promote relaxation of the passengers during a night flight. Equally it can be desirable for the lighting mood to be continuously and slowly varied in order for example to simulate the natural change in light which occurs during a sunrise or sunset.
2. Discussion of the Prior Art
In order to permit a variation of that nature in the lighting situation, light emitting diodes (LEDs) are increasingly used for the interior lighting in an aircraft. In contrast to a fluorescent lamp which is frequently of such a design that it produces white light with a spectral distribution which simulates sunlight, an individual light emitting diode emits light in a comparatively narrow-band spectral range. In order to set a predetermined light colour and in particular to be able to vary that light colour an LED-based lighting arrangement therefore generally uses a combination of light emitting diodes of different colours, for example in the colour combination of red-blue-green. The differently coloured light emitting diodes are actuated in such a way that overall a mixed light of the desired light colour is produced. Conventionally, the individual light emitting diodes of the lighting arrangement are arranged in a succession in a line, the colour of the light emitting diodes changing in a rotational fashion along that arrangement. A problem which frequently occurs in the case of an LED-based lighting arrangement, by virtue of the space conditions which are comparatively limited there, in particular in an aircraft, is that the spacing between the light emitting diodes and the very close wall of the interior to be lit is too small for complete thorough mixing of the light components produced by the individual light emitting diodes to take place over that distance. The consequence of this is that the illuminated wall appears spotty and thus ‘restless’ to the person viewing it. That effect impairs the action of the interior lighting achieved and is thus undesirable.
A further disadvantage which frequently occurs with a conventional LED-based lighting arrangement is that the light emitting diodes of different colours are loaded to differing degrees, especially as in the case of an average lighting situation the red light component dominates whereas green light occupies only a comparatively small proportion of the overall illumination intensity. The comparatively heavy loading of the in particular red light emitting diodes in turn results in premature wear of that kind of light emitting diode, and thus results in the lighting arrangement having a comparatively short service life.